The technical field of the present invention relates to apparatuses for reproducing a recorded image and a special reproduction method therefor.
In recent years, in the television broadcast field, the conventional analog broadcasting is shifting to digital broadcasting.
An object of the invention disclosed in JP-A-2003-257157 is to provide information recording apparatus that is capable of recording broadcast information so that the broadcast information to be reproduced can be correctly identified to reproduce it with increased convenience of the reproduction of the broadcast information. Problem solving means disclosed in JP-A-2003-257157 is as follows: performing time management at the time of reproduction on an allocation unit ALU basis by use of the receiving times of the first packet and the last packet of an allocation unit ALU that includes a plurality of packets included in the broadcast information; and on the basis of display time information of an I picture included in the packet or on the basis of receiving time information of the I picture, performing the time management in question even on an access unit basis including the I picture.
An object of the invention disclosed in JP-A-2005-197839 is to easily enable special reproduction by: at the time of recording a transport stream, inserting positional information of an I picture into the transport stream according to specified rules; at the time of the special reproduction, quickly reading out the positional information of the I picture according to the rules; and detecting the I picture on the basis of the positional information. Problem solving means disclosed in JP-A-2005-197839 is as follows: at the time of recording a transport stream on a recording medium, analyzing the picture type of MPEG to obtain positional information of an I picture; describing the obtained positional information of the anterior I picture in a format of a transport stream packet to make it an I reference packet; periodically (at intervals of a fixed number of packets) inserting the I reference packet into a transport stream to record the I reference packet; and at the time of the special reproduction, obtaining the inserted I reference packet and extracting a transport stream packet of the I picture on the basis of the I reference packet to perform the special reproduction.
In the field of the digital broadcasting, it is possible to use an image compression technology in which video data is compressed to be transmitted. As a practical standard of the image compression technology used in the digital broadcast, the MPEG technology has achieved widespread use.
In the case of the digital television broadcasting that adopts the MPEG technology, data is time-division multiplexed by use of a relatively short transmission unit (transport packet); the time-division multiplexed data is then transmitted from a broadcasting station to a receiver as a MPEG2-TS (transport stream).
According to the MPEG2 standard, audio/visual data (AV data) is encoded; the encoded data is then transmitted as an MPEG2-TS that is constituted of a plurality of transport packets.
The MPEG2-TS which has been received by the receiver is decoded by a decoder. The decoded MPEG2-TS is then output to a display screen and an audio output device as AV data.
In addition, the received MPEG2-TS can also be temporarily stored in a storage medium using a disk, such as a HDD (hard disk drive), an optical disk, a magneto-optical disk, and a magnetic disk. The received MPEG2-TS can also be temporarily written to a recording device or medium that uses a semiconductor (for example, a card-like storage medium). When a viewer wants to view the stored MPEG2-TS, the viewer can reproduce and view the MPEG2-TS through the operation by the viewer. In this case, at the time of the reproduction, the user can perform the special reproduction such as fast forward reproduction, rewind reproduction, and jump reproduction. A recording technology, such as a method for recording MPEG2-TSs on a recording device or medium, is disclosed in, for example, JP-A-2003-257157.
Incidentally, when the MPEG2 is used to encode an image, the MPEG2 has not only a function of directly encoding all frames of image data but also a function of referring to data of an adjacent frame that has already been encoded so that only the difference from that data is encoded. In general, a moving image has a high correlation between frames that are adjacent to each other. Therefore, it is expected that by encoding only the difference between frames adjacent to each other, it is possible to drastically decrease the amount of information created as a result of the encoding.
According to the MPEG standard, frames (pictures) are classified into three picture types: an I (Intra) picture; a P (Predictive) picture; and a B (Bidirectionally predictive) picture.
The I picture is a frame (picture) that keeps independence among GOP (Group of Pictures) and that is encoded without reference to data of other frames (pictures). On the other hand, the P picture is a frame (picture) that is encoded with reference to a past I picture or a past P picture. The B picture is a frame (picture) that is encoded with reference to past and future I pictures or past and future P pictures. Encoding efficiency becomes higher in the order of I, P, and B. Accordingly, the encoding efficiency of the I picture is the lowest. However, the I picture has a feature that it is possible to reconstruct an image by only one frame (picture).
Therefore, when the special reproduction such as fast forwarding is performed, only an I picture is extracted to reconstruct an image. JP-A-2005-197839 discloses a method in which positional information of an I picture is written to a recording medium such as a HDD, and then a transport stream is reproduced by reading out the positional information.
Here, an example of a data structure used when AV stream contents including video data and audio data is recorded on a recording medium will be described with reference to FIGS. 7 to 9.
FIG. 7 is a schematic diagram illustrating an example of a TTS (Time Stamped Transport Stream) packet.
FIG. 8 is a schematic diagram illustrating the relationship between TTS packets and AUs in an AV stream recorded on a recording medium.
FIG. 9 is a schematic diagram illustrating the relationship between AUs, I pictures, and accompanying information thereof, which are included in an AV stream recorded on a recording medium.
As shown in FIG. 7, to the top of a transport packet (TS packet) having a length of 188 bytes based on the MPEG standard, time information (for example, the time at which a receiver receives the transport packet) having a length of 4 bytes is added. Hereinafter, the time information is referred to as “ATS: Arrival Time Stamp.” The transport packet with the time stamp is then written to a recording medium such as a HDD as a TTS (Time Stamped Transport Stream) packet having a length of 192 bytes. The ATS, which is the time information, holds time stamp information when the transport packet has arrived. A TS packet based on the MPEG standard is constituted of: a header having a length of 4 bytes, the header being located at the top of the TS packet; and a payload (or an adaptation field) having a length of 184 bytes, the payload following the TS packet. A packet ID (PID) is recorded in the header. The packet ID is used to identify each packet. In addition, the TS packet has a program map table (PMT) that associates a PID with a program as the MPEG standard. The program map table can be used to distinguish between video data and audio data and can also be used when a broadcast program provider identifies a stream.
As shown in FIG. 8, for example, 8192 TTS packets constitute an AU (Allocation Unit). In this case, the size of each AU is 1.5 M bytes.
Among TTS packets included in an AU is a TTS packet in which a payload of a transport packet includes the above-described I picture.
SI (Stream Information) is information used to manage a search access unit at the time of the reproduction of an AV stream that is recorded on a recording medium on an AU basis. The SI is recorded as a file different from an AU. Information about locations including an I picture and GOP (Group of Picture) are recorded in the SI. In addition, the search access unit at the time of the reproduction is a data unit by which special reproduction can be performed when only the data unit is specified. In order to make it possible to perform the special reproduction, the search access unit includes at least one I picture. A specific example of the search access unit at the time of the reproduction is, for example, GOP that is specified by the above-described MPEG standard.
Also, an AV stream includes contents information that is constituted of video data and audio data.
On the other hand, a file for storing management information of an AU is AUI (Allocation Unit Information). The time at which a first TTS packet of the AU has arrived (for example, the time at which a receiver has received a transport packet) is recorded in the AUI as time stamp information.
FIG. 9 is a diagram illustrating the relationship between AUs, AUI, and SI. The AUI and SI are the time stamp information.
The above-described prior art describes a method in which in order to perform the special reproduction of a MPEG2-TS, positional information of an I picture is recorded on a recording medium in advance, and then the positional information is utilized. To be more specific, the SI file as described above is created, and the SI file is then utilized to achieve the special reproduction of the MPEG2-TS.
Incidentally, the prior art described above does not disclose a method for performing the special reproduction in a case where SI cannot be used. That is because there is also a case where a piece of SI is missing due to a malfunction of an HDD. Usually, SI is optional, and how to deal with it depends on vendors. Therefore, in particular, a case where video data read out from a removable HDD is subjected to the special reproduction presents a problem.
For example, while the special reproduction is performed by use of SI, if the absence of an SI piece is detected within the SI, a malfunction of a display image (for example, a skip) occurs.